Pumped Hydro Energy Storage System and Method

ABSTRACT

A pumped hydro energy storage system and method are disclosed. The system employs a high-density fluid, such as a slurry, to improve power output. In some cases, the fluid is a binary fluid system, with a high-density fluid and a lower-density fluid, such as water. The lower-density fluid flows through the turbine unit of the system, avoiding the need to modify the system to handle the high-density fluid, while achieving improved power output. The system can be configured with one atmospheric reservoir for a higher-density fluid and another one for a lighter-density fluid. Each of them is connected to a pressurized cavity which is filled with the higher-density or lighter-density fluid. The atmospheric tanks may be at the same elevation, or the tank with high density fluid might be higher for increased energy output. For example, the system may be placed on a topographical elevation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/657,941, filed on Apr. 16, 2018; U.S. Provisional Application No62/672,566, filed on May 16, 2018; U.S. Provisional Application No.62/680,597, filed on Jun. 5, 2018; and U.S. Provisional Application No.62/747,678, filed on Oct. 19, 2018, which are incorporated herein byreference in their entirety for all purposes.

FIELD OF THE INVENTION

The present disclosure relates to pumped hydro energy storage system andmethod. In particular, the present disclosure relates to pumped hydroenergy storage system and method using a high-density fluid or acombination of a high-density fluid and a lower-density fluid, such aswater, to increase power output.

BACKGROUND

Renewable energies, such as those harnessed from the sun, wind andwater, are popular forms of energy to generate electricity, since theyhave minimal impact on our environment. For example, renewable energydoes not pollute the environment, such as CO₂ emissions. Althoughrenewable energy has advantages, there are also disadvantages. Forexample, renewable energy is highly dependent on nature, which isundependable or unreliable at best. Solar power requires sunlight, whichcan be affected by clouds; wind power relies on the wind, which can comeand go; water power relies on water, which relies on limited number ofwater ways and has numerous challenges. These unreliability orinconsistencies of renewable energy contribute to imbalances in supplyand demand. Such imbalances cause huge swings in energy pricing.

Conventional pumped hydro energy relies on water flowing down from anupper reservoir to a lower reservoir through a penstock. The water thenturns a turbine to generate electricity which is sent to the grid. Torecharge the upper reservoir, water is pumped up the penstock. Pumpedhydro energy storage, since it has, besides a turbine, a pump torecharge the system, provides controllability and reliability. Thisstabilizes the imbalances of supply and demand which are inherent intraditional renewable energy sources. Furthermore, an importantconsideration for conventional hydro power energy systems and pumpedhydro storage is the footprint required by the reservoirs.

The present disclosure is directed to a small footprint pumped hydroenergy storage system and method with high power output.

SUMMARY

Embodiments generally relate to an unconventional pumped hydro storagesystem and application of the pumped hydro storage system. The systemhas a smaller footprint and higher energy density than conventionalpumped hydro power energy systems. The system uses a high-density fluid,and allows for different configurations where upper and lower reservoirsmay be at the same elevation. Hydraulic pumps and turbines may be placedhigher than the lower reservoir, for example, on the surface above anunderground mine.

In particular, an embodiment relates to a pumped hydro storage systemwhich includes a first reservoir and a second reservoir which isdisposed below the first reservoir. The system also includes a turbineunit. The turbine unit includes a first turbine unit flow port and asecond turbine unit flow port. A penstock is provided which is in fluidcommunication with the first and the second reservoirs. The penstockincludes a first portion which is coupled to the first reservoir and thefirst turbine unit flow port and a second portion which is coupled tothe second reservoir and the second turbine unit flow port. The turbineunit is disposed proximate to the second reservoir. A slurry circulatesthrough the system. The slurry is a high-density fluid which has adensity greater than water. The slurry flows through the turbine in afirst or forward direction from the first reservoir to the secondreservoir to cause the turbine unit to generate energy. In the rechargemode, the slurry flows through the turbine unit in the second or reversedirection from the second reservoir to the first reservoir to rechargethe system. The high-density slurry increases power output of the systemas compared to systems using water.

These and other advantages and features of the embodiments hereindisclosed, will become apparent through reference to the followingdescription and the accompanying drawings. Furthermore, it is to beunderstood that the features of the various embodiments described hereinare not mutually exclusive and can exist in various combinations andpermutations.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of various embodiments. In the followingdescription, various embodiments of the present disclosure are describedwith reference to the following, in which:

FIG. 1 shows a simplified diagram of an exemplary embodiment of a pumpedhydro storage system;

FIG. 2 shows a simplified diagram of an alternative exemplary embodimentof the pumped hydro storage system;

FIG. 3 shows a simplified diagram of another alternative exemplaryembodiment of the pumped hydro storage system;

FIGS. 4a-d show simplified diagrams of alternative exemplary embodimentsof pumped hydro storage systems; and

FIG. 5 shows an exemplary embodiment of a turbine and pumpconfiguration.

DETAILED DESCRIPTION

Embodiments described herein generally relate to a pumped hydro energystorage system. The present pumped hydro energy storage system produceshigher energy output per volume than conventional pumped hydro energystorage systems. In some embodiments, the pumped hydro energy system,unlike conventional pumped hydro energy storage systems, can beimplemented on flat land or even topography.

FIG. 1 shows a simplified diagram of an embodiment of a pumped hydroenergy storage system 100. As shown, the pumped hydro energy systemincludes an upper reservoir 110 and a lower reservoir 120 connected by apenstock 130. In one embodiment, the upper reservoir is disposed abovethe lower reservoir. The difference in elevation or height of the tworeservoirs may be referred to as the head. The penstock is coupled to anupper reservoir port 112 and a lower reservoir port 121. The penstockmay be a pipe, channel or other types of conduits, which provides fluidcommunication between the upper and lower reservoir via the upper andlower reservoir ports. In one embodiment, a turbine unit 140 is disposedproximate to the lower reservoir port. The turbine unit is a reversibleturbine. For example, the turbine is a Francis turbine which serves as apower generator when rotated in a first direction and a pump whenrotated in a second direction. Other types of turbines or turbine unitconfigurations may also be useful. For example, the turbine unit mayinclude a separate turbine for generating power and a pump forrecharging the system. Providing a separate turbine and pump may beparticularly useful for high pressure applications. For example, aFrancis turbine can only operate at 70 BAR. The use of separate turbineand pump configuration can operate beyond 70 BAR.

In operation, fluid contained in the upper reservoir flows through thepenstock to the lower reservoir by gravity. This can be referred to asthe discharging state of the system. As fluid flows through the penstockinto the lower reservoir, it turns the Francis turbine in a firstdirection to generate electricity. The electricity can be transmitted bytransmission lines. For example, in times of energy demand, fluid isflowed from the upper reservoir to the lower reservoir to generateelectricity. The turbine can be rotated in the second direction, pumpingfluid in the lower reservoir up towards the upper reservoir.Alternatively, a pump is used to pump fluid up towards the upperreservoir. This can be referred to as the charging or recharging stateof the system. The system may be recharged in times of low energy demandor when the upper reservoir is empty or near empty.

In one embodiment, the system is a closed system. In a closed system,the reservoirs are enclosed. For example, the reservoirs are fluid tankswhich form a closed loop. The lower reservoir may be referred to as ahigh-pressure reservoir while the upper reservoir may be referred to asa lower pressure reservoir relative to the lower reservoir. In oneembodiment, the upper reservoir may be a cylindrical atmospheric tankwhile the lower reservoir is a high-pressure spherical tank. Otherconfigurations of tanks may also be useful. The reservoirs may includefill ports for filling them with fluids. The tanks may be configured tohave about the same capacity.

The system may be designed with the desired parameters to generate thedesired amount of electricity and when the system needs to be recharged.For example, the flow rate of the fluid which is determined by the sizeof the penstock, the head which is determined by the height between theupper and lower reservoirs, and volume of the reservoirs can beconfigured to determine the power output and recharge time of thesystem. The flow rate and head determine the power output and the volumeof the reservoirs determines the time between recharging.

In one embodiment, the fluid of the pumped hydro storage system is ahigh-density fluid. The high-density fluid has a density of greater thanwater. For example, the high-density fluid may have a density which is≥3x, where x is the density of water. In one embodiment, thehigh-density fluid is a slurry mixture. Various types of slurry mixturesmay be employed. The slurry mixture may include, for example, metaloxide particles mixed with a lower-density fluid, such as water. Othertypes of particles and lower-density fluids may also be useful. Thevolume of particles in the slurry may be equal to or greater than about50%. For example, the percentage of particles may be about 50-85%. Inother embodiment, the percentage of particles may be 50-75%. The higherthe volume of particles, the higher the density of the slurry. Allpercentages are volume percentages. Other percentages may also beuseful.

In one embodiment, the particles of the slurry are submicron in size toavoid damaging the turbine. As for the remaining composition, itincludes a lower-density fluid, such as water. In one embodiment, toprevent the slurry from coalescing and to improve flow, a small amountof surfactant may be added. For example, about less than 1% ofsurfactant can be added. In some cases, antifreeze may be added toprevent freezing of the slurry. The concentration of antifreeze shouldbe sufficient to prevent the slurry from freezing.

In one embodiment, the high-density fluid is a magnetite slurry mixture.The magnetite slurry mixture may achieve a density of 3 to 4 tons/m³,which is more than 3 times of the density of water. Other types ofslurry mixtures, as discussed, can also be employed as the high-densityfluid. The density may depend on the mineral content and composition.

By employing high-density fluid, a more compact pumped hydro energystorage system can be achieved. For a given reservoir or tank volume,the energy storage capacity is proportional to the density of the fluid.For example, in the case where the high-density fluid has a density of3x, the energy storage capacity of the system is 3 times of that whenwater is used. This is due to the mass flow rate being about 3 timesmore than that of water. Alternatively, the system can produce the sameamount of energy output using less volume of fluid and/or less heightdifferential between the upper and lower reservoirs. This results inlower costs as well as more flexibility in designing a system to satisfyoutput requirements.

An advantage, as discussed with using a high-density fluid, is a higherpower output. The use of a high-density fluid can be easily retrofittedinto existing pumped hydro storage systems by modifying the penstock andpump to handle the high-density fluid, thereby increasing the poweroutput. Furthermore, existing designs of hydro storage systems can bemodified to serve as models for highly efficient hydro storage systemswhich handle a high-density fluid. The cost to build, for a given poweroutput requirement, would be reduced due to less volume needed, smallerpenstocks and/or reduced elevation or height between the reservoirs.

FIG. 2 shows a simplified diagram of another embodiment of a pumpedhydro energy storage system 200. The system may include similarcomponents as that described in FIG. 1. Such components may not bedescribed or described in detail.

In one embodiment, the system is a closed system with upper and lowerreservoirs 210 and 220. The reservoirs are fluid communicatively coupledby a penstock 230. As shown, the system is configured as a binary fluidsystem which utilizes first and second fluids 251 and 255. In oneembodiment, the first fluid is a high-density fluid and the second fluidis a lower-density fluid compared to the first fluid. The high-densityfluid, for example, has a density of greater than water. Thehigh-density fluid will have a density which is ≥3.0x, where x is thedensity of water. Other densities for the high-density fluid may also beuseful. The high-density fluid may be a slurry mixture, such as amagnetite slurry mixture. Other types of slurry mixtures or high-densityfluids may also be useful. As for the second fluid, in one embodiment,it is water. For example, the high-density fluid is 3 times denser thanthe lower-density fluid. Providing different density differentialsbetween the fluids may also be useful. The larger the difference, themore efficient the system. Other types of lower-density fluids may alsobe useful.

The penstock 230 includes first and second portions 230 a and 230 bwhich are communicatively coupled to the first and second reservoirs atboth ends and a cavity reservoir 270 coupled to second ends of the firstand second portions of the penstock. In one embodiment, the cavityreservoir is a high-pressure cavity tank. The high-pressure cavity tankshould sustain the overburden pressure of the system. In one embodiment,the high-pressure cavity tank sustains roughly the same pressure as theoverburden pressure of the system. The cavity tank may be a sphericalhigh-pressure cavity tank. Other types of high-pressure cavity tanks mayalso be useful.

In one embodiment, the cavity tank is disposed close to the second orlower reservoir, but at some horizontal distance to ensure overburdenpressure is close to that exerted by the slurry column. A first cavitytank port 271 of the cavity tank coupled to the first portion of thepenstock is disposed at a bottom of the cavity tank while a secondcavity tank port 272 of the cavity tank coupled to the second portion ofthe penstock is disposed at a top of the cavity tank. A turbine unit 240is disposed proximate to a lower reservoir port. The turbine may be aFrancis turbine. Alternatively, the turbine unit may include a separateturbine, such as a Pellton turbine and a pump. Other types of turbinesor configurations of turbine units may also be useful.

In one embodiment, the pressure in the cavity tank is generated by thecolumn of high-density fluid. The lower reservoir can be an atmospherictank. For example, the lower reservoir may be a cylindrical atmospherictank. As for the upper reservoir, it may also be an atmospheric tank.

In operation, the high-density fluid contained in the upper reservoirflows through the penstock to the cavity tank by gravity. The pressurein the cavity tank due to the column of slurry is much higher than thatof the column of the lower-density fluid contained in the lowerreservoir, so it will flow upwards, and then through the injector of theturbine above. The injector port, for example, is the inlet which wateris fed into the turbine. Due to the stark difference in density, thehigh-density fluid remains in the bottom of the cavity tank while thelower-density fluid is disposed above the high-density fluid in thecavity tank. Furthermore, the configurations of the first and secondcavity tank ports are configured to prevent mixing of the first andsecond fluids. As the high-density fluid continues to flow out of thefirst or higher reservoir by gravity, it forces the lower-density fluidupwards back into the second or lower reservoir, causing the turbine torotate to generate electricity. This can be referred to as thedischarging or power generation state of the system. In contrast, inrecharging state, the lower-density fluid (e.g., water) is pumped downinto the cavity reservoir, forcing the high-density fluid back into theupper reservoir. The cavity tank should be configured to accommodate thepressure created by the high-density fluid forcing the lower-densityfluid back into the lower reservoir.

In one embodiment, the system is configured so that the high-densityfluid does not come in contact with the turbine unit. Thisadvantageously avoids configuring the system to handle the high-densityfluids. For example, the particle size of the high-density fluid neednot be in the sub-micron regime to avoid damaging the turbine. Theparticle size of the slurry may be about several microns to severalhundred microns. The particle size of the slurry should have anon-uniform distribution to facilitate higher volume percentage ofparticles in the slurry and flow within the penstock.

FIG. 3 shows an application of the pumped hydro energy storage system ofFIG. 2. The system of FIG. 3 includes common elements as the system ofFIG. 2. Common elements may not be described or described in detail.Illustratively, the system is implemented in a mine located in, forexample, a mountain 305. The mine may be a coal mine. Other types ofmines may also be useful. Implementing the system in a mine hasadvantages as mine shafts deep into the ground 301 exists, therebyreducing construction cost.

The system includes an upper reservoir 210 located close to the top of amountain, creating an elevation difference between a lower reservoir 220located at the base of the mountain, for example, within the mine. Otherlocations of the reservoirs may also be useful. The location may takeadvantage of the terrain and/or existing structures, such as tunnels andshafts. Although the system is implanted in an existing mine,implementing the system in other locations which take advantage of thenatural terrain, such as salt domes or strata, may also be useful.

The upper reservoir is configured to be in fluid communication with thelower reservoir via a penstock 230. A cavity tank 270 is disposed withinthe penstock below the lower reservoir. The penstock includes first andsecond penstock portions 230 a and 230 b. The first penstock portion iscoupled to the upper reservoir port and a first cavity tank port locatedat a bottom of the cavity tank; the second penstock portion is coupledto the lower reservoir port and a second cavity tank port located at atop of the cavity tank. As shown, the first penstock includes first andsecond first penstock subsections 230 a ₁ and 230 a ₂. The firstpenstock subsection is disposed above ground and coupled to the upperreservoir and the second penstock subsection is disposed below groundand coupled to the cavity tank.

In other words, the cavity tank is located below ground. In oneembodiment, a turbine unit 240 is disposed proximate to the lowerreservoir. For example, it is disposed between the penstock and thelower reservoir port. In one embodiment, the turbine unit includes aturbine 354 and a pump 356. The turbine, for example, is a Peltonturbine. Other types of turbines may also be useful. The turbine, forexample, can sustain high pressures of the system.

A high-density fluid 251 is contained in the upper reservoir. Alower-density fluid 255 is disposed in the lower reservoir. Theoperation of the system 300 is similar to that of system 200 of FIG. 2.For example, lower-density fluid flowing into the lower reservoir causesthe turbine to turn in the first direction, generating power. Torecharge the system, the pump pumps the lower-density fluid down to thecavity tank in the second direction, causing the high-density fluid toflow back into the upper reservoir.

Providing the high-pressure cavity tank below ground is advantageous asit can utilize the lithostatic pressure, thereby countering the pressurecaused by the fluid. This reduces the construction costs of the lowerreservoir. In addition, the mountain terrain provides a naturalelevation for the upper reservoir. The height at which the upperreservoir is elevated can be configured based on output requirements.For example, lower elevations may be useful to reduce costs associatedwith building the upper reservoir and penstock if output requirementsare met.

FIGS. 4a-4d show various alternative embodiments of pumped hydro storagesystems. The systems include similar components as the systems of FIGS.1-3. Common elements may not be described or described in detail. Thesystems can be advantageously implemented on flat terrain. For example,the first and second reservoirs 410 and 420 can be disposed at about thesame altitude. These embodiments may be particularly advantageous forimplementation on flat land or floating on deep water. This is contraryto conventional pumped hydro storage systems which require differentheights or altitudes between the upper and lower reservoirs.

Referring to FIG. 4a , an embodiment of a pumped hydro storage system400 a is shown. The system includes first and second reservoirs 410 and420. In one embodiment, the reservoirs are disposed at about the samealtitude or height. For example, the reservoirs are located on a levelground or, in the case of a water application, on a ship or an off-shorerig. Providing the reservoirs at different heights may also be useful.Preferably, the high-density reservoir is located above thelower-density reservoir. The reservoirs are in fluid communication by apenstock 430. As shown, the penstock is a U-shaped penstock. Othershaped penstocks may also be useful. The length of the penstock may befrom hundreds of meters to kilometers long.

The first reservoir serves as a container for the high-density fluid 451and the second reservoir serves to contain the lower-density fluid 455.Due to the higher density of the high-density fluid relative to thelower-density fluid, gravity causes the high-density fluid to flowdownwards, forcing the lower-density fluid up into the second reservoir.This turns a turbine unit 440 disposed proximate to the second reservoirport to generate power. For example, the turbine unit includes acombined turbine-pump, such as a Francis turbine-pump. The systemrecharges by causing the turbine unit to reverse its rotation to thesecond direction. Reversing the direction of the turbine pumps waterdownward, towards the first reservoir. This forces the high-densityfluid back into the first reservoir, recharging the system. In otherembodiments, the turbine unit may include a separate turbine, such as aPelton turbine, and a pump. Other types of turbine or configurations ofturbine units may also be useful.

In one embodiment, the volume of the first or high-density and second orlower-density fluids are configured so that in discharging or chargingstate, the high-density fluid does not contact the turbine. Such aconfiguration advantageously avoids the need to configure the pump tohandle the high-density fluid. This also enables for use of largerparticulates in the slurry, advantageously reducing costs.

FIG. 4b shows another embodiment of a pumped hydro storage system 400 b.The system of FIG. 4b is similar to that described in FIG. 4a . Commonelements may not be described or described in detail.

The system includes first and second reservoirs 410 and 420 which arelocated at about the same altitude or height. Providing the reservoirsat different heights may also be useful. The reservoirs are in fluidcommunication by a penstock 430. As shown, the penstock is a U-shapedpenstock. Other shaped penstocks may also be useful. In one embodiment,the penstock is divided into first and second portions 430 a and 430 b,separated by a cavity reservoir or tank 470, such as that described inFIGS. 2-3. The cavity reservoir, for example, is a sphericalhigh-pressure cavity reservoir. The upper and lower reservoirs may becylindrical shaped atmospheric reservoirs. Other configuration ofreservoirs may also be useful.

Providing a cavity reservoir advantageously increases the fluid capacityof the system. As shown, the cavity tank is disposed below the secondreservoir between the first and second penstock portions. For example,the first penstock portion coupled to the first reservoir is coupled toa first cavity tank port located at a bottom of the cavity tank and thesecond penstock portion is coupled to the second reservoir and a secondcavity tank port located at a top of the cavity tank. This configurationalso reduces the risk of mixing between the high-density andlower-density fluids. The operation of the system is similar to thatdescribed in FIG. 4a , except with an increased capacity due to thecavity tank.

FIG. 4c shows another embodiment of a pumped hydro storage system 400 c.The system of FIG. 4c is similar to that described in FIGS. 4a-4b .Common elements may not be described or described in detail.

The system includes first and second reservoirs 410 and 420 which arelocated at about the same altitude or height. Providing the reservoirsat different heights may also be useful. The reservoirs are in fluidcommunication by a penstock 430. As shown, the penstock is a U-shapedpenstock. Other shaped penstocks may also be useful. In one embodiment,a fluid separator 480 is disposed in the penstock between the first andsecond fluids 451 and 455. The fluid separator, for example, may beformed of a highly abrasion resistant plastic with a density betweenthat of both fluids. For example, the separator floats on thehigh-density fluid while it sinks in the lower-density fluid. The fluidseparator is configured to be slidable within the penstock and maintainsseparation of the high-density and lower-density fluids. Providing aseparator ensures that small particles in the high-density fluid willnot inadvertently be carried up through to the turbine unit. The use offluid separator may also be applied to embodiments described in FIGS.2-3. The system is configured so that the fluid separator does not reachthe turbine 440. The operation of the system is similar to thatdescribed in FIGS. 4a -b.

FIG. 4d shows another embodiment of a pumped hydro storage system 400 d.The system of FIG. 4d is similar to that described in FIGS. 4a-4c .Common elements may not be described or described in detail.

The system includes first and second reservoirs 410 and 420 which arelocated at about the same altitude or height. Providing the reservoirsat different heights may also be useful. The reservoirs are in fluidcommunication by a penstock 430. As shown, the penstock is a U-shapedpenstock. Similar to FIG. 4b , the penstock is divided into first andsecond portions 430 a and 430 b, separated by a cavity reservoir 470,such as that described in FIGS. 2-3. Also, similar to FIG. 4c , a fluidseparator 480 is provided in the penstock to ensure separation of thehigh-density and lower-density fluids. In one embodiment, the cavitytank is configured with a fluid separator cage 475 which ensures thatthe fluid separator can pass through the cavity tank to the first orsecond portion of the penstock. For example, the cage serves as a guidefor the fluid separator while allowing the flow of fluids outside thecage and to maintain separation. The cage may be a set of vertical barsor a perforated pipe with lateral orifices. The cage is configured toenable the fluid separator to flow above and below the cavity reservoir.The operation of the system is similar to that described in FIGS. 4a-c .Furthermore, it is understood that the fluid separator may also beconfigured into the system described in FIGS. 2-3.

FIG. 5 shows an embodiment of a turbine unit 240. As shown, the turbineunit includes a separate turbine 554 and a pump 556. For example, theturbine unit includes separate flow paths or pipes which coupled to thepenstock 230. As shown, the turbine unit includes a pump path 546 and aturbine path 542. For example, in the applications as described in FIGS.2-3 and FIGS. 4a-d , the upper end of the penstock is coupled to thesecond or lower reservoir containing the lower-density fluid while thelower end of the penstock is coupled to the first or upper reservoircontaining the high-density fluid, either directly or indirectly via acavity tank. For example, the upper end of the penstock is the turbineoutlet 561 while the lower end of the penstock is the turbine inlet 562.As discussed, the system is configured so that the high-density fluiddoes not come into contact with the turbine unit. For example, only thelower-density fluid flows through the turbine unit.

In power generation mode, the lower-density fluid, such as water, ispushed through the turbine path upwards toward the lower reservoir, asindicated by the upward arrows. This causes the turbine to turn in thefirst direction, generating power. In recharge mode, the lower-densityfluid is pumped downwards back towards the upper reservoir through thepump path by the pump, as indicated by the downward arrows. This causesthe high-density fluid to be pushed back into the upper reservoir,recharging the system.

As described, the use of a high-density fluid in the system improves thepower output. For example, in the case of a system which employs abinary fluid system with a high-density fluid and a lower-density fluid,such as water, in a flat terrain which involves first and secondatmospheric tanks at the same elevation and a high-pressure cavity tankbelow, such as the systems described in FIGS. 4b and 4d , the pressureat the bottom cavity tank is that exerted by the column of high-densityfluid=c*H*d1 and the pressure at the turbine inlet iscHd1−cHd2=cH(d1−d2), where

-   -   H is the difference in elevation between the first (high-density        fluid) reservoir and the pressurized cavity tank,    -   d1 is the density of the high-density fluid,    -   d2 is the density of the lower-density fluid, and    -   c is a constant.        The power P generated by the system is proportional to the flow        rate Q and to the pressure at the turbine inlet and can be        defined as P=k*Q*cH(d1−d2), where k is a constant. In the case        where the density of the high-density fluid is 3 times of the        lower-density fluid, the use of a binary fluid system increases        power output by about a factor of 2. As described, the use of a        high-density fluid in the system improves power output.

In the case which employs a high-density fluid and a lower-densityfluid, such as water, which includes first and second atmospheric tanksat different elevations and a high-pressure cavity tank below, such asthe systems described in FIGS. 2 and 3, the pressure at the bottompressurized cavity tank is cHd1 while the pressure at the turbine inletis cHd1−chd2, where h is the difference in elevation between the cavitytank and the second (lower-density fluid) reservoir. The power generatedby the system can be defined as P=k*Q*(cHd1−chd2). If H is much greaterthan h, then we get almost as much power if we used high-density fluidalone, but only passing water through the turbine.

The inventive concept of the present disclosure may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. The foregoing embodiments, therefore, are to beconsidered in all respects illustrative rather than limiting theinvention described herein. Scope of the invention is thus indicated bythe appended claims, rather than by the foregoing description, and allchanges that come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A pumped hydro storage system comprising: a first reservoir; a secondreservoir, the second reservoir disposed below the first reservoir; aturbine unit, the turbine unit includes a first turbine unit flow portand a second turbine unit flow port; a penstock which is in fluidcommunication with the first and the second reservoirs, the penstockincludes a first portion which is coupled to the first reservoir and thefirst turbine unit flow port and a second portion which is coupled tothe second reservoir and the second turbine unit flow port, wherein theturbine unit is disposed proximate to the second reservoir; a slurrycirculating through the system, wherein the slurry comprises ahigh-density fluid, and wherein the high-density fluid comprises ahigh-density slurry which has a density greater than that of water;wherein the slurry flows through the turbine unit in a first directionfrom the first reservoir to the second reservoir to cause the turbineunit to generate energy and the slurry flows through the turbine unit ina second direction from the second reservoir to the first reservoir torecharge the system; and wherein the high-density slurry increases poweroutput of the system as compared to water.
 2. The system of claim 1wherein the high-density slurry comprises a density which is ≥about 3times of that of water.
 3. The system of claim 2 wherein the poweroutput of the system is ≥about 3 times when using the high-densityslurry instead of water.
 4. The system of claim 1 wherein thehigh-density slurry comprises a magnetite slurry with magnetiteparticles.
 5. The system of claim 4 wherein a volume percent ofmagnetite particles in the magnetite slurry is about 50%.
 6. The systemof claim 5 wherein a volume percent of magnetite in the magnetiteparticles in the magnetite slurry is about 50-85%.
 7. The system ofclaim 4 wherein a particle size of magnetite particles in the magnetiteslurry is in a sub-micron regime.
 8. A pumped hydro storage systemcomprising: a first reservoir, wherein the first reservoir is configuredto contain a high-density fluid and includes a first reservoir flow portdisposed at a bottom of the first reservoir; a second reservoir, whereinthe second reservoir is configured to contain a lower-density fluidwhich has a density lower than that of the high-density fluid, andincludes a second reservoir flow port disposed at a bottom of the secondreservoir; a cavity tank disposed at a cavity tank elevation, whereinfirst and second elevations of the first and second reservoirs arehigher than the cavity tank elevation of the cavity tank, wherein thecavity tank is configured with an upper cavity tank port and a lowercavity tank port, wherein the upper cavity tank port is disposed abovethe lower cavity tank port; a turbine unit, the turbine unit includes afirst turbine unit flow port and a second turbine unit flow port,wherein the second turbine unit flow port is coupled to the secondreservoir flow port; a penstock, wherein the penstock includes a firstportion penstock coupled to the first reservoir flow port and the lowercavity tank port, wherein a lowest port of the first portion penstock isbelow the cavity tank, and a second portion penstock coupled to theupper cavity tank port and the first turbine unit flow port; wherein inpower generation mode, the high-density fluid is configured through thepenstock towards through the cavity tank and towards the firstreservoir, forcing the lower-density fluid to flow through the turbineand into the second reservoir, the lower-density fluid turns the turbineunit in a first direction to generate power, and in recharge mode, theturbine unit pumps the lower-density fluid from the second reservoirthrough the penstock towards the first reservoir, forcing thehigh-density fluid back into the first reservoir; and wherein thelower-density fluid and high-density fluid are configured to prevent thehigh-density fluid from passing through the turbine unit.
 9. The systemof claim 8 wherein the first elevation of the first reservoir is higherthan the second elevation of the second reservoir.
 10. The system ofclaim 8 wherein the first and second elevations of the first and secondreservoirs are at about the same altitude.
 11. The system of claim 8wherein the first and second reservoirs comprise cylindrical atmospherictanks.
 12. The system of claim 8 wherein the high-pressure cavity tankcomprises a spherical high-pressure cavity tank.
 13. The system of claim8 wherein the high-density fluid comprises a slurry with particles. 14.The system of claim 8 wherein the high-density fluid comprises water.15. The system of claim 8 wherein the high-density fluid has a densitywhich is at least 3 times greater than that of the lower-density fluid.16. The system of claim 8 wherein the slurry comprises metal oxideparticles.
 17. The system of claim 8 wherein the slurry comprisesmagnetite particles to form a magnetite slurry.
 18. The system of claim16 wherein: the slurry comprises 50-85% particles; and sizes of theparticles range from several microns to several hundred microns.
 19. Amethod for generating power from a pumped hydro storage systemcomprising: providing a first reservoir containing a high-density fluid,a second reservoir containing a lower-density fluid, a cavity tankdisposed at a cavity tank elevation which is below a first reservoirelevation of the first reservoir and a second reservoir elevation of thesecond reservoir, a turbine unit coupled proximately to the secondcavity tank, and a penstock to provide fluid communication within thesystem; in power generation mode, flowing the high-density fluid fromthe first reservoir towards the second reservoir to force thelower-density fluid into the second reservoir which turns the turbine ina first direction to generate power; in recharging mode, pumping, by theturbine unit, the lower-density fluid towards the first reservoir toforce the high-density fluid into the first reservoir to recharge thesystem; and wherein when the lower-density fluid and high-density fluidcirculate through the system, the high-density fluid is configured toavoid passing through the turbine unit.
 20. The method of claim 19wherein the high-density fluid has a density which is at least 3 timesgreater than that of the lower-density fluid.